1. Field of the Invention
This invention relates to methods for improving flow of hydrocarbons through conduits, particularly pipelines. The invention also relates to methods for making improved drag reducing agents, and preferably, to methods for making ultra-high molecular weight amorphous polymers and copolymers of alpha olefins with improved drag reducing properties, having inherent viscosities in excess of about 10 dL/g.
2. Description of Related Art
Generally speaking, the flow of liquid in a conduit, such as a pipeline, results in frictional energy losses. As a result of this energy loss, the pressure of the liquid in the conduit decreases along the conduit in the direction of the flow. For a conduit of fixed diameter, this pressure drop increases with increasing flow rate. When the flow in the conduit is turbulent (Reynold""s number greater than about 2100), certain high molecular weight polymers can be added to the liquid flowing through the conduit to reduce the frictional energy losses and alter the relationship between pressure drop and flow rate. These polymers are sometimes referred to as drag reducing agents (xe2x80x9cDRAsxe2x80x9d), and they interact with the turbulent flow processes and reduce frictional pressure losses such that the pressure drop for a given flow rate is less, or the flow rate for a given pressure drop is greater. Because DRAs reduce frictional energy losses, increase in the flow capability of pipelines, hoses and other conduits in which liquids flow can be achieved. DRAs can also decrease the cost of pumping fluids, the cost of equipment used to pump fluids, and provide for the use of a smaller pipe diameter for a given flow capacity. Accordingly, an ongoing need exists to formulate improved drag reducing materials.
While various polymerization methods and reactants have been published in the patent literature, most of those methods do not yield specialized polymers with properties that make them effective as drag reducers. Many of the methods, for example, produce non-amorphous polymers. e.g., solid or crystalline polymers. Other methods yield polymers with molecular weights that are much too low to be useful in drag reduction. Still other methods yield polymers having poor drag reducing properties. For example, some commercially available polymers are deficient when used with highly viscous crude oil, where the need may be the greatest. In certain aspects, the present invention overcomes one or more of the above-mentioned shortcomings.
While alkylaluminoxane has been used in certain polymerization processes, the inventors are not aware of any patents or publications showing alkylaluminoxane being used to make drag reducing agents (DRAs) in general, or, more specifically, to make amorphous, ultra-high molecular weight polyalphaolefin polymers with the superior drag reducing properties of the present invention. For example, U.S. Pat. Nos. 5,436,212; 5,298,579; 5,070,160 and 4,659,685 disclose certain uses of alkylaluminoxane, but do not disclose or suggest the present invention.
The present invention is directed to methods of improving the flow of hydrocarbons through conduits, particularly viscous crude oil flowing through pipelines. Surprisingly, it has been discovered that a drag reducing agent (DRA) made in accordance with the methods of this invention can produce as much as about thirty percent (30%) or greater flow improvement when added to a hydrocarbon flowing through a conduit. Advantageously, such flow improvement can result when the drag reducing agent""s polymer is added to the hydrocarbon at a concentration of as low as 1 part per million (ppm) by weight.
In certain aspects, the invention also relates to methods of producing amorphous, ultra-high molecular weight drag reduction agents having unexpectedly superior drag reduction properties when combined with liquid hydrocarbons, such as viscous crude oil. In another aspect, the invention is directed to a composition of matter, including an amorphous drag reduction agent with an ultra-high average molecular weight, far in excess of ten million, with inherent viscosities in excess of about 10 dL/g.
Broadly, one aspect of the invention involves a method of producing an amorphous polyalphaolefin mixture containing an ultra-high molecular weight polyalphaolefin polymer with an inherent viscosity of at least about 10 dL/g and surprisingly superior drag reducing properties when combined with crude oil that is flowing through a pipeline or other conduit. The method preferably includes the steps of contacting a reactant mixture that includes alpha olefin monomers with a transition metal catalyst and an alkylaluminoxane co-catalyst, to provide an amorphous polyalphaolefin mixture containing an ultra-high molecular weight polyalphaolefin polymer with an inherent viscosity of at least about 10 dL/g and surprisingly superior drag reducing properties when used with viscous crude oil. The polyalphaolefin mixture can be introduced to a pipeline or other conduit having flowing hydrocarbons, such as viscous crude oil. The polyalphaolefin DRA mixture should be introduced in an amount sufficient to increase the flow of the flowing hydrocarbons, preferably at a concentration of from about 1 to 250 ppm by weight, and more preferably from about 25 to 150 ppm by weight.
A specific embodiment of the invention is directed to a method for forming a drag reducing agent comprising a non-crystalline, ultra-high molecular weight polyalphaolefin having an inherent viscosity of at least about 10 deciliters per gram, by contacting alpha olefin monomers with a catalyst system that includes a transition metal catalyst and a co-catalyst mixture that includes an alkylaluminoxane co-catalyst; and polymerizing the alpha olefin monomers at a temperature at about or less than about 25xc2x0 C.; wherein, during the polymerization, at least a portion of the alpha olefin monomers polymerize in the reactant mixture to provide an ultra-high molecular weight polyalphaolefin.
In another specific embodiment of the invention, the polymerization is terminated by adding a xe2x80x9cdeactivatorxe2x80x9d to the reactant mixture after at least a portion of the alpha olefin monomers polymerize in the reactant mixture, to provide an amorphous, ultra-high weight polyalphaolefin. One example of a deactivator is a mixture of isopropyl alcohol and butylated hydroxytoluene.
A variety of alpha olefin monomers are useful in this invention, including homopolymers, copolymers and terpolymers, which can be present in the reactant mixture in different amounts, alone or in combination. Preferably, these monomers are present at a charge rate of about 4% to 22% based on total weight of the reactant mixture. Charge rate is herein defined as the weight percent of total charge including solvent, co-catalyst, catalyst, and alpha olefin monomers. More preferably, these monomers are present at a charge rate of 8% to 20% based on total weight of the reactant mixture. Examples of alpha olefin monomers that are useful in this invention are co-monomers of 1-hexene and 1-dodecene alpha olefins; or co-monomers of 1-octene and 1-tetradecene alpha olefins in a 1:1 ratio based upon mole weight of the monomers.
A preferred transition metal catalyst is titanium trichloride, which is preferably present in the reactant mixture in an amount of from about 100 to about 1500 parts per million, preferably from about 150 to about 400 parts per million, based on the total weight of all the reactants or components in the reactant mixture.
A further feature of the process for forming a drag reducing agent comprising a non-crystalline, ultra-high molecular weight polyalphaolefin having an inherent viscosity of at least about 10 deciliters per gram is that the reactant mixture may include at least one hydrocarbon solvent such that the alpha olefin monomers and polyalphaolefin remain substantially dissolved in the hydrocarbon solvent. An additional feature of the process is that the polymerization of the alpha olefin monomers continues such that the polyalphaolefin is present in the reactant mixture at a concentration of at least about 4 weight percent based upon the weight of the reactant mixture and the polyalphaolefin having an inherent viscosity of at least about 10 deciliters per gram is formed in less than about 12 hours. Another feature of the process is that the polyalphaolefin has an inherent viscosity of at least about 10 deciliters per gram and is amorphous with substantially no crystalline particles. A further feature of the process is that the flow increase is at least about 30% when the polyalphaolefin is present in hexane at a weight concentration of 1 part per million. Another feature of the process is that the catalyst system may include dibutylaluminum chloride and/or diethylaluminum chloride.
In another specific embodiment, the present invention includes a drag reducing agent comprising a non-crystalline, ultra-high molecular weight polyalphaolefin having an inherent viscosity of at least 10 deciliters per gram, formed by contacting alpha olefin monomers with a catalyst system in a reactant mixture, wherein the catalyst system includes a transition metal catalyst, such as titanium trichloride, and the co-catalyst mixture includes an alkylaluminoxane co-catalyst, such as methylaluminoxane and isobutylaluminoxane; and polymerizing the alpha olefin monomers at a temperature at about or less than 25xc2x0 C., preferably less than 10xc2x0 C., wherein during the polymerization, at least a portion of the alpha olefin monomers polymerize in the reactant mixture to provide a non-crystalline, ultra-high molecular weight polyalphaolefin.
In yet another specific embodiment, the present invention includes a process for reducing drag in a conduit by forming a drag reducing agent comprising a non-crystalline, ultra-high molecular weight polyalphaolefin, by contacting alpha olefin monomers with a catalyst system in a reactant mixture, wherein the catalyst system includes a transition metal catalyst and an alkylaluminoxane co-catalyst; polymerizing the alpha olefin monomers at a temperature at about or less than 25xc2x0 C., preferably less than 10xc2x0 C.; wherein during the polymerization, at least a portion of the alpha olefin monomers polymerize in the reactant mixture to provide a non-crystalline, ultra-high molecular weight polyalphaolefin having an inherent viscosity of at least 10 deciliters per gram; and introducing the drag reducing agent into the conduit.
In still another aspect of the invention, a halohydrocarbon co-catalyst may be used in conjunction with a transition metal catalyst to form the drag reducing agent. For example, another specific embodiment of the invention is directed to a process for forming a drag reducing agent comprising a non-crystalline, ultra-high molecular weight polyalphaolefin having an inherent viscosity of at least about 10 deciliters per gram. The process includes the steps of contacting alpha olefin monomers with a catalyst system in a reactant mixture, wherein the catalyst system includes a transition metal catalyst and a co-catalyst mixture having at least two co-catalysts, wherein one of the co-catalysts preferably is a halohydrocarbon. More preferably, the co-catalyst mixture also includes alkylaluminoxane. The alpha olefin monomers are polymerized at a temperature at about or less than 25xc2x0 C., wherein during the polymerization, at least a portion of the alpha olefin monomers polymerize in the reactant mixture to provide a non-crystalline, ultra-high molecular weight polyalphaolefin.
A further feature of the process for forming a drag reducing agent comprising a non-crystalline, ultra-high molecular weight polyalphaolefin having an inherent viscosity of at least about 10 deciliters per gram is that the halohydrocarbon is preferably a chloride containing halohydrocarbon such as ethylene dichloride. Another feature of the process is that the transition metal catalyst is preferably titanium trichloride. An additional feature of the process is that the catalyst system preferably includes an alkylaluminoxane such as methylaluminoxane and/or isobutylaluminoxane.